Coiled tubing has been used for decades in land-based hydrocarbon recovery operations to perform various well treatment, stimulation, injection, and recovery functions more efficiently than with threaded tubulars. In a conventional land-based operation, the coiled tubing injector may use a gear drive mechanism with conventional bearing assemblies to reliably and efficiently transmit power to the coiled tubing.
While conventional coiled tubing injectors may work satisfactorily for land-based or shallow-water operations, they would not work in deeper water because the drive mechanism for the injector is not sufficiently protected from the subsea environment. Specifically, the hydrostatic pressure at such depths is sufficient to penetrate past the seals used on lubricated components such as the gear case and bearing assemblies of land-based equipment. A proposed solution to this problem is disclosed in U.S. Pat. No. 4,899,823, whereby the tubing injector is protected subsea by an enclosure surrounding substantially the entire tubing injector. Seals are provided between the enclosure and the coiled tubing above and below the injector. An obvious disadvantage of this solution is the size of the housing and complexity of enclosing the entire injector with the housing.
An improved coiled tubing injector for subsea use is therefore desirable.